1. Field of the Invention
The present invention relates to an organic electroluminescent (EL) display device, and more particularly, to an organic electroluminescent display device having improved structures of electrodes and an encapsulation layer and an external light reflection prevention structure.
2. Description of the Related Art
Recently, much attention has been paid to electroluminescent display devices because they have advantageous features suitable for next generation display devices, such as a wide viewing angle, a high contrast ratio and a high response speed. Electroluminescent display devices are classified into inorganic electroluminescent display devices and organic electroluminescent display devices according to materials to form emitter layers.
At the beginning of the development of inorganic electroluminescent display devices, they were put into commercial use as green-emitting display devices. However, inorganic electroluminescent display devices, like plasma display devices, are driven under an AC bias condition and require drive of several hundreds of volts. Also, since light-emitting materials for the inorganic electroluminescent display devices are inorganic matter, it is difficult to control light emission wavelength characteristics through molecular design, so that full-color display of a picture is not easily achieved.
On the other hand, organic electroluminescent display devices are spontaneous emission display devices that emit light by electrically exciting fluorescent organic compounds. Thus, it is expected that organic electroluminescent display devices can be applied to next generation display devices that can overcome shortcomings of liquid crystal display devices, with characteristics including low driving voltage, enabling the production of thin, small display panels, wide viewing angle, high response speed and so on. Organic electroluminescent display devices using a layered structure have been developed by Eastman Kodak Company and have been commercialized as green-emitting display devices having improved lifetime by Pioneer Electronic Corporation.
Recently, many kinds of new materials having various molecular structures that are advantageous in organic materials, and organic electroluminescent display devices (to be abbreviated as organic EL devices, hereinafter) as color display devices having excellent characteristics including lower DC drive voltage, small and thin structure, spontaneous emission and so on, have been the subjects of active research.
An example of an organic EL device is disclosed in Japanese Patent Publication No. Hei 10-335060 and is shown in FIG. 1.
Referring to FIG. 1, an organic EL device 10 is configured such that an organic layered structure 11 is disposed between an anode 12 and a cathode 13, and the cathode 13 is protected by an encapsulation layer 14 containing aluminum and at least one material having a work function greater than that of aluminum.
In the conventional organic EL device having the above-described configuration, external light is reflected by the cathode 13 and the encapsulation layer 14, degrading readability of an image. In particular, in an outdoor environment in which the organic EL device is exposed to sunlight, relative luminance and contrast are sharply degraded by external light reflected by the cathode 13.
U.S. Pat. No. 5,059,861 discloses an organic EL device having a cathode formed of various kinds of metals, excluding alkaline metals.
U.S. Pat. No. 5,047,687 discloses an organic EL device having a cathode formed of various kinds of metals including at least one metal having a low work function, excluding alkaline metals. Here, the metals include aluminum, vanadium and cobalt.
Japanese Patent Publication No. Hei 9-274990 discloses an organic EL device having an encapsulation layer that encapsulates an anode, an organic layered structure and a cathode, the encapsulation layer having at least one dehydrating agent selected from the group consisting of silica gel, zeolite, calcium chloride, activated carbon, nylon and polyvinyl alcohol.
U.S. Pat. No. 5,073,446, Japanese Patent Publication Nos. Hei 5-36475, Hei 8-222368 and Hei 7-161474 disclose organic EL devices having an anode, an organic layered structure, a cathode, an encapsulation layer to protect the cathode, and a sealing layer.
Most conventional EL devices use a polarizing film on the surface of a substrate in order to prevent reduction in the luminance of an image due to reflection of external light by electrodes and an organic layered structure. However, the use of a polarizing film results in shielding of some light generated from the organic layered structure, causing a substantial decrease in luminance.
Accordingly, it is an object of the present invention to provide an organic EL device which can enhance the contrast and luminance of an image and can remove the necessity of using a polarizing film to reduce the reflection of external light.
The foregoing and other objects of the present invention are achieved by providing an organic EL device comprising: a transparent substrate; a first electrode unit formed on the transparent substrate in a predetermined pattern and made of a transparent conductive material; an organic EL unit including organic layers having a predetermined pattern, stacked on the first electrode unit; a second electrode unit corresponding to the first electrode unit, formed on the organic EL unit in a predetermined pattern; and an encapsulation layer to encapsulate the first electrode unit, the organic EL unit and the second electrode unit to protect the same, the encapsulation layer consisting of a first component and a second component made of one or more metals selected from the group consisting of iron (Fe), cobalt (Co), vanadium (V), titanium (Ti), aluminium (Al), silver (Ag) and platinum (Pt).
In an embodiment of the present invention, the first component of the organic EL device is at least one transparent material selected from the group consisting of SiOx (x greater than 1), SiNx (x greater than 1), MgF2, CaF2, Al2O3, In2O3, and ITO (Indium Tin Oxide), and the encapsulation layer has a gradual component concentration gradient is distributed such that the light absorption efficiency of the encapsulation layer gradually increases along the thickness direction of the encapsulation layer as the distance of the encapsulation layer from the surface upon which external light is incident increases.
The foregoing and other objects of the present invention may also be achieved by providing an organic EL device comprising: a transparent substrate; a first electrode unit formed on the transparent substrate in a predetermined pattern and made of a transparent conductive material; an organic EL unit including organic layers having a predetermined pattern stacked on the first electrode unit; a second electrode unit formed on the organic EL unit consisting of a first component and a second component made of one or more metals selected from the group consisting of iron (Fe), cobalt (Co), vanadium (V), titanium (Ti), aluminium (Al), silver (Ag) and platinum (Pt); and an encapsulation layer to encapsulate the first electrode unit, the organic EL unit and the second electrode unit.
The foregoing and other objects of the present invention may also be achieved by providing an organic EL device comprising: a transparent substrate; an external light absorbing layer formed on the transparent substrate to absorb external light, a second electrode unit formed on the external light absorbing layer, an organic EL unit formed of organic layers having a predetermined pattern and stacked on the second electrode unit, and a first electrode unit formed on the organic EL unit in a predetermined pattern.
In an embodiment of the present invention, the external light absorbing layer includes a first component made of at least one transparent material selected from the group consisting of SiOx (x greater than 1), SiNx (x greater than 1), MgF2, CaF2, Al2O3, In2O3, and ITO (Indium Tin Oxide), and a second component made of one or more metals selected from the group consisting of iron (Fe), cobalt (Co), vanadium (V), titanium (Ti), aluminium (Al), silver (Ag) and platinum (Pt). Also, in an embodiment of the present invention, the external light absorbing layer is configured to have a gradual component concentration gradient.
The foregoing and other objects of the present invention may also be achieved by providing an organic EL device comprising: a substrate; a pixel area having anode layers formed on the substrate in a predetermined pattern; an organic EL unit having organic layers stacked on the respective anode layers; an insulating protective layer formed on the substrate to open the organic EL device, and cathode layers formed on the organic EL unit and protective layer in a predetermined pattern, and a drive area having thin film transistors (TFTs) formed on the substrate to selectively apply a predetermined voltage to the anode layers, wherein the anode layers are formed of external light absorbing layers.
The foregoing and other objects of the present invention may also be achieved by providing an organic EL device comprising: a transparent substrate, a buffer layer formed on the transparent substrate, a thin film transistor (TFT) layer formed on the buffer layer, an intermediate insulator layer to cover the TFT layer, a transparent electrode layer formed on the intermediate insulator layer in a predetermined pattern and to which voltages are selectively applied by TFTs, an insulating protective layer having an opening to open the transparent electrode layer, an organic EL unit having organic layers stacked on the transparent electrode layer, and a cathode layer formed on the organic EL unit and the insulating protective layer in a predetermined pattern, wherein an external light absorbing layer is formed between the intermediate insulator layer and the insulating protective layer, excluding an area corresponding to the organic EL unit.
The foregoing and other objects of the present invention may also be achieved by providing an organic EL device comprising: a transparent substrate; a buffer layer formed on the transparent substrate; a thin film transistor (TFT) layer formed on the buffer layer; an intermediate insulator layer to cover the TFT layer; a transparent electrode layer formed on the intermediate insulator layer in a predetermined pattern and to which voltages are selectively applied by TFTs; an insulating protective layer having an opening to open the transparent electrode layer; an organic EL unit having organic layers stacked on the transparent electrode layer; and a cathode layer formed on the organic EL unit and the insulating protective layer in a predetermined pattern, wherein the cathode layer includes a first component which is a transparent material and a second component made of one or more metals selected from the group consisting of iron (Fe), cobalt (Co), vanadium (V), titanium (Ti), aluminium (Al), silver (Ag) and platinum (Pt).
The foregoing and other objects of the present invention are also achieved by providing a method of preparing an organic EL device comprising: preparing a transparent substrate; forming a first electrode unit formed on the transparent substrate in a predetermined pattern; forming an organic EL unit including organic layers having a predetermined pattern, stacked on the first electrode unit; forming a second electrode unit formed on the organic EL unit to drive the organic EL unit with the first electrode unit; and forming an encapsulation layer to encapsulate the first electrode unit, the organic EL unit and the second electrode unit, the encapsulation layer including a first component formed of a transparent material and a second component formed of a metal, the first and second components having a gradual component concentration gradient.
In this embodiment, the forming of an encapsulation layer includes injecting a mixture of 3-50 wt % of SiO, which is a transparent material, and 50-97 wt % of at least one metal selected from the group consisting of Fe, Co, V, Ti, Al, Ag, Cu and Pt, the SiO and the metal having different melting points, into a deposition boat, and depositing SiO and the metal while gradually raising the temperature of the deposition boat to form the encapsulation layer.